Conventionally cord filaments have a round cross-section, i.e. a cross-section which fits substantially into a circle, though the use of shaped filaments, for instance flat wires, is gaining acceptance in the tire reinforcement field. It is common to provide the filaments with a thin coating of an alloy including at least copper and zinc, which increases the adhesion level of the filament with elastomeric material, particularly during the vulcanization process.
It has been observed, that when pneumatic tires reinforced by steel cords are cut or punctured, the exposed cord rapidly deteriorates upon contact with corrosive liquids, such as salt solutions or water. The liquid enters the cut or puncture and rapidly progresses along the entire length of cord destroying the tire assembly. It is believed that one reason for this deterioration is an imperfect rubber penetration through the twisted cord during the vulcanization step of the tire. The resulting voids within the cord construction facilitate the penetration of the corrosive liquid along its length. A complete rubber penetration into the inside of the cord also suppresses the risk of filament migration within the cord.
In order to avoid the above problems, a great number of so-called open cords or rubber penetrating constructions, wherein a rubber layer is interposed between the steel filaments, has been proposed. Open cord constructions like 2+2, 3+1, 2.times.1 have been successful in the passenger tire field. However, in case of multilayered structure cords, as are required to reinforce the elastomeric material of light-truck and truck tires, it has up to now not been possible to develop a cord construction allowing a complete penetration of the elastomeric material into the inner core of the cord.